The invention relates to a magnetic-tape apparatus comprising a rotatably drivable capstan for driving the magnetic tape and comprising a pressure-roller device which comprises a pressure roller to be pressed against the capstan, a movable pressure-roller support, a pressure-roller spindle carried by the pressure-roller support, and a substantially rotationally symmetrical bearing member arranged on the pressure-roller spindle for rotatably supporting the pressure-roller spindle, an inner bearing surface being associated with the pressure roller and the bearing member having an outer bearing surface adapted to cooperate with the inner bearing surface, and the inner bearing surface associated with the pressure roller and the outer bearing surface of the bearing member each having a curved shape allowing the pressure roller to perform a pivotal movement to adapt the axial direction of the pressure roller to the axial direction of the capstan.
Such an apparatus of the type defined in the opening paragraph is known from, for example, DE-GM 1,793,121. In this known apparatus the inner bearing surface associated with the pressure roller and the outer bearing surface of the bearing member both have a substantially spherical shape. The inner bearing surface associated with the pressure roller is formed by a first bearing-surface part provided on an annular portion of the pressure roller and by a second bearing-surface part provided on a dome-shaped insert, a pressure spring acting upon the insert to press the insert against the bearing member mounted on the pressure-roller spindle, i.e. against the outer bearing surface of this bearing member. This results in a comparatively intricate construction comprising several parts and the spring load urging the insert against the bearing part has the disadvantage that between the insert and the bearing member a comparatively high static friction is produced which must be overcome when the pressure roller performs a pivotal movement to adapt the axial direction of the pressure roller to the axial direction of the capstan, so that not a continuous but only an abrupt pivotal movement can be realised, which is not beneficial for an undisturbed tape drive. Moreover, the pivotal movement of the pressure roller in the known apparatus is performed about a pivotal centre which is situated exactly in the centre of the spherical bearing surfaces, i.e. coincides with the axis of the pressure roller. This results in a comparatively large distance between the pivotal centre and the contact surface of the capstan against which the pressure roller is urged, which is rather likely to give rise to a non-uniform and asymmetrical force and pressure distribution between the capstan and the pressure roller applied to it in the axial direction of this roller, as a result of which the part of the magnetic tape between the capstan and the pressure roller is loaded in the axial direction of this roller and consequently the magnetic tape is urged out of its tape path necessary for a correct operation, which may lead to tape damage and tape-transport problems and is therefore undesirable.